Servo braking apparatus



July 3o, 1957 s. H. EDGE =ET AL SERVO BRAKING APPARATUS Filed July 14, 1954 nvenlor By (Nn-M L, llorneys nited States Patent SERV() BRAKING APPARATUS Stanley Howard Edge and Frederick Leslie Beet, Lincoin, England, assignors to Clayton Dewandre Company Limited, Lincoln, England, a British company Application July 14, 1954, Serial No. 443,394 Claims priority, application Great Britain July 20, 1953 4 claims. (cl. so-sms) This :invention relates to servo-assisted brake-operating mechanisms for road-vehicles and particularly to such mechanisms of the kind wherein the output of a vacuum or compressed-air servo device employing a piston or diaphragm as the pressure-responsive operating member is transmitted hydraulically to the brake-actuating cylinders of the road wheels of the vehicle. g

The object of the invention is to provide `an improved and simplified mechanism of theV above kind which is of compact construction and which is designed to facilitate manual operation of the brakesin the event of the servo device becoming inoperable.

According to the invention there is provided a servoassisted brake-operating mechanism of the kind described including a vacuum or compressed-air servo device controlled by a pedal or like actuated valve means and mounted at one end of and in alignment with an hydraulic cylinder which is adapted to be connected to the brakeactuating cylinders, Iand means extending through said servo device into the hydraulic cylinder and adapted to operate therein as a displacement device, said means being operable to transmit to the liquid in the hydraulic cylinder effort produced by the servo device and manual effort applied to the pedal or like actuator, but being movable independently of the operating member of the servo device so that, in the event of the latter being in an inoperable condition, manual effort can be transmitted by said means to the liquid in the hydraulic cylinder without any obstruction or interference from said operating member of the servo device.

Reference will now be made to the accompanying drawing which illustrates in sectional elevation a preferred embodiment of the invention in its inoperative condition.

In the embodiment illustrated in the drawing, the servoassisted brake-operating mechanism includes an hydraulic cylinder 1 formed at one end (hereinafter regarded as the forward end of the mechanism) with an outlet port 2 which is adapted to be connected with the brake-actuating cylinders of the road wheels of thevehicle. At the other end of the hydraulic cylinder there is arranged a vacuum servo device 3 consisting of a piston 4 mounted within a cylinder 5 to the forward end wall 6 of which the hydraulic cylinder lis coaxially fixed.

Extending concentrically through the servo cylinder into the hydraulic cylinder and slidably supported thereby is a displacement device 7. This device includes an elongated, hollow, cylindrical outer component 8V whose forward end portion projects into the interior of the hydraulic cylinder 1 through a chamber 9formed at the rear thereof. This chamber is provided with a port 10 which is adapted to be connected by a conduit (not shown) with Ia source of vacuum. The chamber is separated from the interior of the hydraulic cylinder by a wall or partition 11 formed with a central aperture through which the component 8 is slidably guided. A sealing gland12 is arranged against the forward face of the wall 11 so as to ensure that no liquid escapes along the outer surface of said component.

Within the components there is mounted an inner component formed in two parts 13 and 14. The rear part 13 is of hollow cylindrical form and is slidably supported in the rear portion of the outer component 8, and the forward part 14 is of tubular form and projects coaxially from the front end of the rear part through a portion 15 of reduced internal diameter formed in the central part of the outer component 8. The forward part 14 of the inner component extends with clearance through the reduced portion 15 of the outer component f.. CC

`to leave an annular passage 16 between its outer surface and the inner surface of Said reduced portion. The part 14 is slidably guided in the reduced portion 15 by means of one or more external projections 17. The shoulder at the forward end of said reduced portion forms an annular valve seat 18 for a disc valve element 19 which is mounted in a valve chamber 20 formed in the outer component 8 at the forward`r end of the reduced portion thereof. This valve chamber is provided with ports 21 opening into the vacuum chamber 9. The valve element 19 is biassed onto its seat by a coil spring 22 held in compression between the valve element and a slotted plug 23 which is screwed into the forward end portion of the outer component 8 to form the valve chamber 20V. and to seal oi Vthe interior of the displacement device from the interior of the hydraulic cylinder 1. The disc valve element is guided in its opening and closing movement by the wall of the valve chamber and is formed with peripheral recesses 24 to permit the passage of air past the valve element when it is unseated.

In the rear part 13 of the inner component there is iitted a cup-shaped member 25 which forms a socket for engagement by the end of a rod 26 connected with the brake pedal of the vehicle. This cup-shaped member is formed with ports 27 through which the interior of said inner component is at all times open to atmosphere via the rear end of the outer component, a central opening 28 in the rear end wall of the servo cylinder, and the space within the cylinder to the rear of the piston 4, which space is in constant communication with atmosphere through a breather 29 in the rear end Wall of the cylinder. A exible gaiter 30 is preferably providedto prevent dust or dirt entering the mechanism, the gaiter being fixed at one end to a ferrule 30a slidably mounted on the rod 26, and at the other end to an annular member 31 attached to the rear end wall of the servo cylinder.

In its central portion the servo piston is formed with a rearwardly projecting sleeve 32 within which is tted a sealing sleeve 33 which in turn iits on the outer component 8 of the displacement device. This sealing sleeve permits axial movement of said outer component independently of the servo piston whilst maintaining a i'luidtight seal between the two.

Forwardly of the servo piston the displacement device carries a reaction device by means of which a progressive control of the servo output is established; that is to say, it ensures that the effort produced by the servo piston, which effort is dependent upon the degree of vacuum -to which the piston is subjected, is proportional to the manual effort applied to the pedal. The reaction device consists of a number of beams 34 which lie in substantially radial planes with respect to the displacement device and the servo piston and each of which is pivotally mounted intermediate its ends upon a radial arm 35 tixed to orl When the mechanism is in its inoperative condition, as shwn in the dawing, the inner component occupies a rearward positioriwhe'rein the front end of its forward part 14 is disengaged from the disc valve element 19 which consequently. remains seated on4 the annular valve seatw18.A In this condition;V theV space within the siervo, cylinderforward of the piston is open toA atmosphereA via the* openings 37, the annular passage, 16 the interiorof the inner lcomponent of the displacement device, the ports 27 in the cup-shaped member 25,Y the rear end .of` the outercornponent of the displacement device, the opening 28m the rear end walll of the servo cylinder, the space to the rear of the servo piston, and the breather 29. Thus, with both of its sides under atmospheric pressure, thek servo piston remains at rest.

When the operator depresses the brake pedal hiseffort; is transmitted through the rod 26 to theinner component ofthe displacement device, which component is thereby advanced firstly to engage the. disc valve4 element 19 and so cut off the forward space of thetservo. cylinderfrom atmosphere, and thereafter to unseat thedise valve element so that said spaceis placed in communication withI the sourceA of vacuum via the valve chamber 20, the portsv 21 and the vacuuml chamber9. The resulting pressure differential in the servocylinder. advances theservo piston whose movement is transmitted through. the reaction beams 34 and` theirsupporting arms 35 to the outer component of the displacement device so. as to advance said component further into the Vhydraulic cylinder. The resulting displacement of vliquid from this cylinder causes the operation of thebrakes. Return'springs 38 and 39 are provided forthe servok piston andthe displacement device respectively` As the output elfortof the servoA piston is transmitted to the outer component of the displacement device through the reaction beams, this effort reacts through the beams against the inner component of the displacement device and, therefore, against the manual effort applied to the brakefpedal, thus givingvthe operator a feel'of the degree to which his own effort is being power-assisted. The reaction is proportionateV to the servo output, being governed by the ratio' between the two arms of each. beam either side of its fulcrum. Since the reaction is proportionate the relation between the inputand output ef-l forts is proportionate also. For example, when the effortproduced by the servo pistonI exceeds the manual input effort the inner component of the displacement device is moved rearwardly bythe inneriends ofthe beams and allows thendiscvalve element 19 to be seated and thus cut off thevfo'rwardspaceof therservo cylinder from vacuum. Ifthe inputeffort is Vmaintained constant at this point they valveelem'ent will assume a lapped condition in which it is in engagement with the valveseat 18 and is in turn engaged by the forward end of the inner component of the :displacement device. If, on the other hand, the input effort is reduced, said inner component will be moved further in the rearward direction with the result that its forward end will become disengaged from the disc valve element and admitatmosphere to the forward space ofthe -servoA cylinder. This space will remain open to atmosphere until the balance between input and outputv is restored, when the valve element will again resume its lapped condition. tween the manual input effortv and the loutput effort `produced by the servo` is maintained-toY give arprogressive control of the servo. output.

IfV the manualdinput effort exceeds the maximum re.

active force that can b e exerted by the servo piston through the beams, which iswhen the servo piston is subjected to full vacuum, the innercomponentof the displacement deviceis advanced to a point where a number of external projections 40 on its forward part 13 abut a shoulder 41 formed on the inner surface of theouter component 8 atv the rear end of the reduced portion 15` Thus the proportion beplication of vacuum to the servo piston is then fully opened. 'lhereaftenv any increase in the input effortr will not produce a corresponding increase in the servo assistance, and the manual effort will be transmitted through the displacement device to the liquid in the hydraulic cylinder 1, thus being added to the effort produced by the servo piston.

In the event of the servo device being inoperable in any way, such as, for example, if no vacuum is available, the manual effort is transmitted directly to the liquid in the hydraulic cylinder by the displacement device without any obstruction or interference from the servo piston, such as, for example, the cushioning effect which might otherwise be caused by the piston being moved in the servo cylinder when no vacuum is beingapplied. This is made possible by the fact that the displacement device extends slidably through the servo piston and is thus movable independently thereof.

FOP feplenshtina the. liquid. in the hydraulicv cylinder a reservoir (n otl shown) is,` provided. The-reservoirfcommunicatesvia ayport 42K in the wall of the cylinder with an annular space 43 formed,` between the sealing gland 12 and an; annular recuperative sealY 44 surroundingthe forward end of the/outerV component 8 of the displacement device. In its inner periphery they seal is formed with an annular recess 45 whichV opens rearwardly towards the annular space43. The seal is backed by a perforated annular washer 46 between which andthe. seal thereis interposedanannular shimi47 formedwith radialgrooves or ribs 48 to permit liquidpassing through the perfora-` tions in the `washer 46toreach the vannular recess 45 in the seal. Intheforward end of. the outer component 8 of the displacement device-there is formed a` number of radial ports 49=which, when said Outer component is inits fully/,retractedlposition,register with the annular recess 4S to permit replenishment` of the hydraulic cylinder with liquid from the reservoir via the annular space 43. When theA outer-.component of thedisplacement device is advanced intothe interiorl ofithehydraulic cylinder during the operation.of:`.theA mechanism, the radial ports 49-are moved.y forwardly of theseal 44v and the latter prevents any `liquid escaping `back into the annularl space 43.

In order to .improve its sealing-qualities the seal- 44-is formedon its` forward face with two-concentric` lipsl 50 which areradapted-to be pressed into sealing contactiwith the inner. surface of the-cylinder and the outer surface ofthe outer Vcomponent-.ofthe displacement device respectively by pressure created within theV interior of the cylinder.-

The seal is -held in place by a perforated sleeve 51 one end of which bears against -the forward end of the cylinder and the other end of which engages in the annular recess between thetwo concentric lips 50 of the seal. A similar sleeve 52'is provided for holding the sealing gland 12 in place.

We claim:

1. A-servo-,assisted brake-operating mechanism comi prisinga hydraulic brake master-cylinder having means for connecting. it to the brakes, a differential huid-pressure energized-rservo-device mounted at one end ofthe hydraulic cylinder and in alignment therewith, an assembly extending movablythrough the servo-device in axial alignment .therewith and with the. hydraulic cylinder` and comprising. a hollowouter member having a` closed end-extendingintd the hydraulic cylinder. and reciprocable thereinto displacehydrauliciluid therefrom toqthe brakes, and a hollowmanually operable inner memberk m'onted coaxially within the f outen member and reciprocable axially thereinand having,means ,engageable withl the.A

outer member-to transmit movement thereto in hydraulic fluid displacingdirectiom the outer. member having a valve seat thereinfand the inner member-having an open endv located adjacentl to said valve seat, means operative in response to relative axial movement betweensaid inner and outer members for,cont rolling-the operation.

of the servo-device including a valve within the outer member and positioned for engagement with said valve seat of the outer member or with the open end of the inner member, and means connecting the servo-device to said outer member for operation thereof and engageable with the inner member -for transmitting thereto reaction of the servo-device.

2. A servo-assisted brake-operating mechanism, comprising a hydraulic master cylinder having means for connecting it to the brakes for transmitting hydraulic pressure thereto, a servo-device having a differential iluid pressure energized operating element mounted at one end of the hydraulic cylinder and in alignment therewith, an assembly extending through the operating element of the servo-device in axial alignment therewith and with the hydraulic cylinder and comprising a hollow outer member having a closed end forming a ram extending into the hydraulic cylinder and reciprocable therein to displace hydraulic fluid therefrom to the brakes and provided with an axial bore having means of communication with one side of the operating element of the servo-device, and a hollow manually operable inner member movable axially within the outer member and having means thereon engageable with the outer member to move it in hydraulic uid displacing direction, said inner member being open at one end to provide communication between the interior of the inner member and the bore of the outer member, and the outer member having a valve seat therein located in proximity to said open end of the inner member, means operative in response to relative axial movement between said members for controlling the operation of the operating element of the servo-device including a valve having a spring acting to engage it with said valve seat and said valve being engageable by said open end of the inner member to interrupt communication between the interior of the inner member and the erating element of the servo-device to said outer member for operation thereof in hydraulic fluid displacing direction and for transmitting reaction from the servo-device to said manually operable inner member.

3. A servo-assisted brake-operated mechanism as defined in claim 2, wherein said hydraulic cylinder is formed with an annular space for replenishing said cylinder with hydraulic uid, and including an annular recuperative seal fixed within said hydraulic cylinder and surrounding the outer member of said assembly, the inner periphery of said seal being formed with an annular recess which communicates with said annular space, and wherein the Outer member of said assembly is provided with a port which registers with said annular recess in said seal when said outer member is retracted to thereby provide communication for the passage of hydraulic iluid from said annular space to the interior of the hydraulic cylinder and which port is beyond said seal when said outer member is advanced to thereby prevent back flow of hydraulic fluid to said annular space.

4. A servo-assisted brake-operating mechanism as defined in claim 3, wherein said seal is formed in one face with two concentric lips which are pressed into sealing contact with the inner surface of said hydraulic cylinder and the outer surface of the outer member of said assembly by the pressure of hydraulic uid in said cylinder.

References Cited in the tile of this patent UNITED STATES PATENTS 2,130,799 Hofstetter Sept. 20, 1938 2,458,803 Stelzer Ian. 11, 1949 2,532,960 Stelzer Dec. 5, 1950 

